JPH0886570A - Fixed bed type filtration preheater for high-temperature treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of contaminated matter in exhaust gas by a method wherein volatile substance in exhaust gas is condensed to adhere the same to glass forming particles, then, heated glass forming particles are sent from a preliminary heater into a glass melting zone, and purified exhaust gas is discharged out of the preliminary heater. SOLUTION: Low-temperature glass forming particles are supplied to a preliminary heating vessel 4 to form the fixed bed 9 of glass forming particles in a filtrating zone 20, then, high-temperature exhaust gas 1 is conducted to flow through a gas cooling zone 14 to reduce the temperature of the high-temperature exhaust gas 1 at least by 200 deg.F by the radiation of heat to the glass forming particles. Thereafter, the exhaust gas 1 is conducted to flow through the fixed bed 9 from the gas cooling zone 14 while maintaining the fixed condition of the fixed bed 9 as it is whereby particular substance is filtrated from the exhaust gas 1 into the fixed bed 9 while the fixed bed 9 is heated to condense volatile substance in the exhaust gas 1 and adhere the same to the glass forming particles, then, the heated glass forming particles 12 are sent from a preliminary heating vessel 4 into a glass melting zone 8, and purified exhaust gas is discharged out of the preliminary heating vessel 4.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to the field of high temperature furnaces, and more particularly to glass making with the step of melting a glass forming material.

[0002]

BACKGROUND OF THE INVENTION Conventional glass melting furnaces use air-fired burners to melt glass-forming materials. The glass melting furnace is one of the highest operating temperatures of any industrial furnace, as it requires very high temperatures to melt the glass forming materials. At such a high operating temperature, a large amount of the heat generated by the burner is lost through the flue (exhaust pipe). In the case of burners fueled by ambient air and natural gas, typically only about 15-20 percent of the energy created by the burner is utilized in the glass melting furnace as useful heat.

The prior art addresses this problem by passing the exhaust gas (flue gas) from the glass melting furnace in an indirect heat exchange relationship with the new incoming air, thereby causing otherwise smoke. Attempting to return the heat that would have been lost through the road to the glass melting furnace. Heat exchangers used for this purpose (referred to as recuperative heat exchangers or recuperators)
Significantly improves the efficiency of commercial air-fired glass melting furnaces.

Nitrogen oxides called NOx are harmful environmental pollutants, and it is an important goal to reduce NOx emission amount. The conventional air-burning glass melting process is a large source of NOx for two reasons.
First, because almost 80 percent of air is nitrogen,
A large amount of nitrogen is introduced into the combustion process to produce NOx.
Second, the high temperatures themselves required for the glass melting process kinetically favor NOx production.

It is well known that the thermal efficiency of glass melting processes can be increased by using oxygen or oxygen-enriched air as the oxidant. Moreover, the use of oxygen or oxygen-enriched air reduces the amount of nitrogen present in the combustion zone by the molecular equivalent of oxygen. However, in the glass melting process using oxygen as an oxidant, although the thermal efficiency is increased by oxygen, the cost of oxygen is high, and therefore the cost is higher than the conventional glass melting process using air as an oxidant. There are many.

Recent advances in the field of glass melting include the method disclosed in US Pat. No. 4,973,346, wherein the glass forming material is preheated before being introduced into the melting vessel.

Although preheating of cullet, or recycled waste glass, has been successfully employed in commercial air-fired glass melting furnaces in recent years, it has limited its commercial success in preheating batch raw materials. There are some difficulties. One drawback is that some of the glass forming materials tend to agglomerate or sinter in the preheater at 538 ° C.
Even the glass-forming material preheated at temperatures below (1000 ° F) impedes its smooth flow.
Another disadvantage is that fine raw materials are entrained in the exhaust gas and increase the dust concentration in the exhaust gas, thus requiring a large investment in pollutant control equipment installed in the exhaust gas conduit.

In glass melting furnaces which use oxygen or oxygen-enriched air, the high temperatures of the exhaust gas pose a further technical difficulty. State-of-the-art cullet and batch feedstock preheaters are designed to treat the exhaust gas from an air-fired melting furnace through a recovery heat exchanger or recuperator to a relatively low temperature before processing. Normally, the maximum inlet temperature of exhaust gas is
Below 816 ° C (1500 ° F). The hot exhaust gas must be cooled by dilution with cooling air or by a heat exchanger. This not only reduces the overall thermal efficiency, but also increases the complexity of the device.

[0009]

Accordingly, there is a need for an improved process that overcomes the problems associated with conventional preheaters. It is an object of the present invention to provide a system with an efficient preheater that significantly reduces the amount of pollutants in the exhaust gas.

[0010]

In order to solve the above problems, according to one aspect of the present invention, there is provided a method for preheating glass forming particles, comprising: A high temperature exhaust gas containing a condensable volatile substance is generated, and (B) the high temperature exhaust gas from the glass melting zone is passed into a preheating vessel that constitutes a gas cooling zone and a filtration zone, and (C) low temperature glass. Forming particles are fed into the preheater to form a bed of glass forming particles in the filtration zone, (D) hot exhaust gas is passed through the gas cooling zone, and heat radiation to the glass forming particles causes Reducing the temperature of the hot exhaust gas by at least 200 ° F. (112 ° C.), and (E) allowing exhaust gas from the gas cooling zone to flow through the bed while maintaining the bed of glass forming particles in a fixed state; in addition Thus filtering the particulate matter from the exhaust gas to the bed and heating the bed to condense volatile substances from the exhaust gas and deposit them on the glass forming particles,
(F) A method is provided that comprises sending the heated glass forming particles from the preheater to the glass melting zone and discharging purified exhaust gas from the preheater.

According to another aspect of the present invention, there is provided a glass melting apparatus comprising (A) a glass melting container, (B) a preheating container constituting a cooling zone and a filtration zone, and (C) glass forming particles. Supply means for supplying into the preheater,
And (D) means for forming a fixed bed of glass-forming particles in the filtration zone of the preheater, and (D) exhaust gas from the glass melting vessel through a cooling zone of the preheater and then the filtration. An apparatus is provided comprising: means for exiting the preheater through a bed of glass forming particles in the zone; and (E) means for delivering glass forming particles from the preheater to the glass melting vessel. It

As used herein, the term "condensable volatile substance" means
It means a substance that is in a gas state in the glass melting container and in a liquid or solid state in the preheater. "Hot exhaust gas" has a temperature above 1500 ° F (816 ° C) and, if condensable volatiles are present, maintains at least some condensable volatiles in the gaseous state. Exhaust gas at a temperature high enough to do so. "Cold glass-forming particles" refers to glass-forming particles at a temperature low enough to maintain at least some condensable volatiles in a liquid or solid state. “Bed” refers to a permeable aggregate of solid particles retained within a container. "Fixed bed" or "immobile bed" refers to a bed of non-fluidic particles.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The structure of the present invention will be described below with reference to the accompanying drawings. Referring to FIGS. 1 and 2, a high temperature exhaust gas 1 is generated in a glass melting container or a glass melting zone 2. Zone 2 may be the zone of a glass melting furnace. At least a part of the high-temperature exhaust gas 1 includes a fuel such as natural gas and oxygen-enriched air having an oxygen concentration of 30% or more,
Or by combustion with practically pure oxygen having an oxygen concentration above 99.5%. The use of oxygen or oxygen-enriched air reduces the nitrogen ballast that occurs when air is used as the oxidant, and thus reduces the volume of exhaust gas produced, which is described below in connection with the preheater. Effectively through the bed (flow through the bed of glass-forming particles), enabling the advantageous effects of the invention to be achieved.

Combustion of the fuel and oxidant (oxygen or oxygen-enriched air) is accomplished by a burner not shown, preferred burners for which are US Pat. Nos. 5,076,779 and 5,267,850. Described in. The hot exhaust gas generated by combustion supplies heat to the glass melting zone and heats the particles of glass-forming material (also simply referred to as "glass-forming material", "glass-forming particles", "glass raw material" or "particles"). To melt. Typically, the temperature of the hot exhaust gas exceeds about 1316 ° C (2400 ° F) and is generally 1093-1649 ° C (2000-3).
000 ° F). The hot exhaust gas is composed of nitrogen and combustion products (carbon dioxide, water vapor, etc.).

In the process of melting the glass-forming material in the glass-melting zone 2, the hot exhaust gas captures the particulate matter and the condensable volatile substances from the glass-forming material. Specifically, such particulate substances are, for example, small particles in glass raw materials, and the condensable volatile substances are, for example, sodium sulfate, sodium hydroxide and sodium metaborate.

The high temperature exhaust gas containing the particulate matter and the volatile substance is passed through the glass melting zone 2 through the passage 3 into a gas cooling zone (a zone for cooling the high temperature exhaust gas, also simply referred to as "cooling zone") 14 and a filtration zone ( Filtering particulate matter and condensed matter from the exhaust gas) 20 to a preheating vessel or chamber 4. The passage 3 has a small cross-sectional area in order to minimize the heat transfer (heat radiation) by radiation, but the pressure drop is 2.54 cm (1 in) based on the water column.
Must be large enough to stay below.

In the preferred embodiment shown in FIG. 2, the preheating vessel 4 is formed integrally with a conventional glass melting furnace (glass melting vessel 2) and has a molten glass bath 8 in common with the glass melting furnace. Are configured as separate zones of the glass melting furnace. Alternatively, as shown in FIG. 3, the preheating vessel 4 may be physically formed separately from the glass melting furnace and communicated with the glass melting furnace by an exhaust gas duct. The low temperature glass forming particles 6 are also supplied into the preheating container 4 through the supply means. These glass-forming materials may typically include one or more materials such as sand, soda ash, limestone, dolomite, red bean and cullet or scrap glass. The low temperature glass forming material is generally supplied at ambient temperature.

The low temperature glass forming material is typically deposited in the preheat vessel 4 on the support 7 as two or more beds 9. The multiple beds loaded with material and discharged independently of each other may be arranged one above the other as shown in FIG. 2 or horizontally. The bed 9 of glass-forming particles is
As shown in FIG. 1, a part of the boundary between the cooling zone 14 and the filtration zone 20 can be configured, and the side wall is configured to increase the area of the floor exposed to the high temperature exhaust gas. Good.

In the embodiment shown in FIG. 2, the floor 9
Are formed on each horizontal support 7 by sending particles 6 through a rotary valve 15 and pushing them onto each horizontal support 7 by a feed pusher or charge 13. The high-temperature exhaust gas is made to flow into the cooling zone 14 by a suction draft fan, an eductor, or the like, and is sucked out through the floor 9 from there.

1 and 2 the surface of the bed 9 is angled (tilted) with respect to the flow of exhaust gas through the bed 9.
A preferred floor arrangement is shown. This sloping floor arrangement creates an open surface exposed to hot exhaust gases by forming a floor material (glass-forming material or glass-forming particles)
The floor 9 provides the unique advantage of protecting the metallic support 7 and pusher 13 from hot exhaust gases. In this case, the angle of the floor is an angle close to the repose angle of the charging material (glass-forming material supplied to the floor) in a normal state in order to make the thickness of the floor uniform. Further, in order to form a bed having a uniform thickness, a mechanical vibrating means for smoothing the flow of the bed material (bed particles) may be used. The bed thickness is selected to provide good filtration efficiency without causing excessive pressure drop.

By passing the hot exhaust gas through the preheating vessel 4, many advantageous effects are obtained. First
In addition, when the high temperature exhaust gas passes through the cooling zone 14,
The heat from the hot exhaust gas is radiatively transferred therein to the glass forming material and the walls of the container 4, thereby preheating the glass forming material and improving the thermal efficiency of the glass melting process. This radiative heat transfer is directed not only to the low temperature glass forming particles forming the bed 9, but also to the heated glass forming particles 1 suspended above the molten glass bath 8.
It is also directed to 2. In order to achieve efficient radiant heat transfer from the hot exhaust gas to the glass forming material, it is important to increase the open gas space, increase the surface area of the floor, and improve the heat insulation of the container wall.

Second, this radiative heat transfer reduces the temperature of the exhaust gas by at least 93 ° C. (200 ° F.), preferably at least 260 ° C. (500 ° F.), usually 81
Lower to temperatures below 6 ° C (1500 ° F). The exhaust gas whose temperature has been lowered in this way is then discharged through the bed 9. As the exhaust gas passes through the bed 9, the particulate matter in the exhaust gas is filtered from the exhaust gas and adsorbed on the bed 9, so that the bed is further heated by conduction heat transfer from the exhaust gas. At the same time, the condensable volatile substances in the exhaust gas are condensed and adsorbed on the bed from the exhaust gas.

Some of the bed particles congeal or sinter, which is advantageous in that it improves the bed's filtration activity (the action of filtering particulate matter and condensed matter from the exhaust gas).
Once one bed 9 is heated to the desired temperature, the exhaust gas passage (not shown) downstream of that one bed is closed by keeping the exhaust gas flow through the other bed continuous. Stop the flow of exhaust gas to one bed. The preheated one-bed glass-forming material is then replaced by a new glass-forming material by the charger 13.
A reverse purge gas flow can be used during the charging operation to prevent dust from being entrained in downstream passages in the bed.

As a result of the heat transfer, condensation and filtration described above, three independent beneficial actions are achieved simply, simultaneously and efficiently. That is, both the particulate matter and the condensable volatile matter are removed and purified, and the cooled exhaust gas 1
0 is discharged from the preheating container 4 through the exhaust means 11. On the other hand, the preheated glass forming particles 12 are sent into the glass melting zone 2 through the passage 3. The heat from the exhaust gas is effectively used to preheat these particles.

The present invention differs from conventional preheating systems used in conjunction with furnaces such as glass melting furnaces in that the bed 9 of particles is a fixed or immobile bed during the heating process. In conventional moving bed systems, the bed particles re-release the particulates and condensates once they have been trapped from the exhaust gas by the movement of the bed particles. Therefore, even if some of the particulate matter in the exhaust gas is removed, the particulate material re-released by the moving bed escapes to the exhaust gas duct.

Another problem encountered by the glass manufacturing industry is that the glass-forming particles soften or partially melt due to direct contact of the glass-forming particles with the hot exhaust gas in the preheater. This softening or partial melting of the glass-forming particles makes handling such as transporting the glass-forming particles extremely difficult. The present invention cools the hot exhaust gas to 816 ° C (1500 ° F), for example, by radiative heat transfer in the gas cooling zone integrated with the filtration zone before the hot exhaust gas directly contacts the particle bed in the filtration zone. By overcoming this problem. Moreover, the particular bed design shown in FIG. 2 allows some melting of the particles at the surface of the bed.

The system of the present invention is advantageous because it practically uses pure oxygen or oxygen-enriched air as the oxidant for combustion producing exhaust gas, thereby reducing the volumetric flow rate of the exhaust gas. Generally, the flow rate of exhaust gas in the case of carrying out the present invention is 3 to 5 times as much as that of an equivalent glass melting system except the above-mentioned characteristic part of the present invention.
Twice as low.

The average particle size of the glass forming particles forming the floor 9 is preferably in the range of 0.1 to 5 mm. Smaller particle sizes improve bed filtration and heat transfer characteristics, but increase pressure drop through the bed,
The operating power cost of the process becomes high.

Since the glass-forming material has different physical properties as a filtration medium depending on its type, the components of the glass-forming material used to form the filter bed are preferably selected so as to be suitable for the filter bed. For example, the raw batch material used to form the filter bed is typically prepared to a particle size of less than 1 mm. The cullet can be crushed to have a particle size of 1 to 5 mm and used as a floor material to reduce the pressure drop. The sand used in the raw batch material is
It typically comprises about 60-70% by weight and has excellent solids flow properties and temperature stability. Therefore, it is possible to use only sand as the filter medium and mix the sand that has been preheated by being used as the filter bed with the other glass-forming material and load it into the glass melting furnace.

The preheat vessel can also be designed to maximize heat transfer from the hot exhaust gas to the walls of the preheat vessel, thereby increasing heat transfer to the low temperature glass forming material. Periodic multi-bed systems with mechanical chargers are preferred because they have less technical difficulties in operation than continuous moving beds. As shown in FIG. 1, the system in which the preheating vessel 4 is integrated with the glass melting vessel 2 and the preheated glass forming material 12 is directly charged onto the molten glass bath 8 is A further advantage is that virtually no heat is lost during the normal material transfer time to the glass melting furnace.

In the embodiment shown in FIG. 3, the preheating vessel 60 is provided with a gas cooling zone 61 and a filtration zone 65. In the cooling zone 61, the high temperature exhaust gas 62
Is the flow of the low temperature glass-forming particles 63 (shower).
Flow through and achieve radiative heat transfer to particles 63 and a high percentage of convective heat transfer. Particles such as glass forming material form a vertical or suspended fixed bed 64 within the filtration zone 65, and the exhaust gas flows through the fixed bed 64.

The exhaust gas 68 thus purified is exhausted from the preheating container 60 through the exhaust pipe 66, while
The preheated glass forming materials 67 and 69 are sent to the glass melting furnace from the cooling zone 61 and the filtration zone 65, respectively. The glass forming materials 67 and 69 can be selected from one or more components in the overall formulation for glass making, which materials are mixed before or during feeding to the glass melting furnace. be able to. For example, it is possible to use only sand as the particles 63 and only cullet as the medium for the fixed bed 64. Although not shown in FIG. 3, in order to continuously treat the exhaust gas, it is necessary to install two or more fixed beds 64 and perform periodic operation.

[0033]

The following are specific numerical examples for the purpose of illustrating the present invention. A three-bed cyclic system similar to the system shown in Figures 1 and 2, respectively, was used. Using a low temperature glass forming material consisting of a typical soda lime glass batch with a cullet content of 35%, 7.432 m ²
It has a surface area of (80 ft ² ) and a surface area of 15.24 cm (6i
A bed was formed with an average depth of n). The average particle size of the glass forming material was 0.5 mm.

Natural gas and practically pure oxygen 8,60
At a temperature of 1577 ° C. (2870 ° F.) generated by burning at a heat release rate of 10,000 BTU / hour, the hot exhaust gas containing particulate matter and sodium sulfate is passed through the cooling zone and about 538 ° by heat radiation. C (10
Cooled to a temperature of 00 ° F). The gas was then passed through the bed at an average velocity (pressure drop 215.9 mm water column) of 3.1 m / min (0.17 ft / sec).
The bed particles were preheated to an average temperature of about 482 ° C (900 ° F). The surface temperature of the floor is approximately 538 ° C (1
000 ° F). The cooled and purified exhaust gas is
The temperature was 260 ° C (500 ° F), and it was found that 99% of the particulate matter was removed by passing through the bed and almost all of the sodium sulfate was removed by comparison with the newly introduced high temperature exhaust gas. It was

It can also be applied to other high temperature furnaces such as cement kilns or lime kilns or furnaces for processing iron ore or pelletized material. Even in such applications, the present invention provides that, except that the condensable volatiles are not present,
It can be operated in the same manner as for glass production. A rigorous definition of such a method would be: A method for preheating particles, comprising:
(A) generating high temperature exhaust gas containing particulate matter in the furnace zone, and (B) passing the high temperature exhaust gas from the furnace zone into a preheating vessel forming a gas cooling zone and a filtration zone,
(C) feeding cold particles into the preheater to form a bed of particles in the filtration zone, (D) passing hot exhaust gas through the gas cooling zone, and by heat radiation to the particles The temperature of the hot exhaust gas is at least 200 ° F. (112
° C) and (E) allowing exhaust gas from the gas cooling zone to flow through the bed while keeping the bed of particles stationary, thereby filtering particulate matter from the exhaust gas to the bed. Heating the bed, and (F) sending the heated particles from the preheater to the furnace zone and discharging purified exhaust gas from the preheater.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the structures and forms of the embodiments illustrated herein, and deviates from the spirit and scope of the present invention. It should be understood that various embodiments are possible and that various changes and modifications can be made.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of the system of the present invention.

FIG. 2 is a schematic cross-sectional view of one embodiment of the system of the present invention.

FIG. 3 is a schematic cross-section of a preheater according to the invention with a gas cooling zone with flowing batch material.

[Explanation of symbols]

 1: Hot exhaust gas 2: Glass melting vessel or zone or furnace zone 4: Preheating vessel or chamber 5: Supplying means 6: Low temperature glass forming particles 7: Support 8: Molten glass bath 9: Fixed bed 10: Cooled exhaust gas 12: Heated particles 13: Pusher or charging device 14: Gas cooling zone 20: Filtration zone 60: Preheating vessel 61: Gas cooling zone 62: High temperature exhaust gas 63: Low temperature glass forming particles 64: Fixed bed 65: Filtration Zone 67: Preheated glass forming particles 69: Preheated glass forming particles

Claims (13)

[Claims] 1. A method for preheating glass-forming particles, comprising: (A) generating high temperature exhaust gas containing a particulate material and a condensable volatile material in a glass melting zone; and (B) melting the glass. The hot exhaust gas from the zone is passed through a preheating vessel that constitutes a gas cooling zone and a filtration zone, and (C) low temperature glass-forming particles are fed into the preheater to remove glass-forming particles in the filtration zone. Forming a bed, (D) allowing hot flue gas to flow through the gas cooling zone, and lowering the temperature of the hot flue gas by at least 200 ° F. (112 ° C.) by radiating heat to the glass-forming particles, (E) Exhaust gas from the gas cooling zone is passed through the bed while keeping the bed of glass-forming particles fixed, thereby filtering particulate matter from the exhaust gas to the bed and heating the bed. Then, a volatile substance is condensed from the exhaust gas and deposited on the glass-forming particles, and (F) the heated glass-forming particles are sent from the preheater to the glass melting zone and purified from the preheater. A method comprising discharging the exhaust gas discharged. 2. At least a portion of the hot exhaust gas is generated by combustion of a fuel and an oxidant having an oxygen concentration of at least 30%.
The method described in. 3. The hot exhaust gas is caused to flow through the floor at an angle to the surface thereof.
The method described in. 4. The method according to claim 1, wherein the hot exhaust gas is passed through a downflow of glass-forming particles in the gas cooling zone. 5. The bed of glass-forming particles in the filtration zone consists primarily of sand, including the step of feeding the sand heated by the hot exhaust gas to the glass melting zone along with other glass-forming materials. The method of claim 1 characterized. 6. A glass melting apparatus, comprising: (A) a glass melting container, (B) a preheating container constituting a cooling zone and a filtration zone, and (C) a glass forming particle supplied into the preheating device. Means for forming a fixed bed of glass-forming particles in the filtration zone of the preheater, and (D) exhaust gas from the glass melting vessel in a cooling zone of the preheater. Means for discharging the preheater through the bed of glass forming particles in the filtration zone, and (E) means for sending glass forming particles from the preheater to the glass melting vessel. A device consisting of. 7. The apparatus of claim 6 including means for passing a downflow of glass-forming particles through said cooling zone. 8. A method for preheating particles comprising: (A) generating high temperature exhaust gas containing particulate matter in a furnace zone, and (B) converting the high temperature exhaust gas from the furnace zone into a gas cooling zone. (C) supplying low temperature particles into the preheater to form a bed of particles in the filtration zone; and (D) hot exhaust gas into the gas cooling zone. Through the gas cooling zone to reduce the temperature of the hot exhaust gas by at least 200 ° F. (112 ° C.) by heat radiation to the particles, and (E) the gas cooling zone with the bed of particles kept stationary. Exhaust gas from the exhaust gas is passed through the bed, thereby filtering particulate matter from the exhaust gas to the bed and heating the bed, and (F) delivering the heated particles from the preheater to the furnace zone. From the preheater Method consisting in discharging the reduction has been the exhaust gas. 9. At least a portion of the hot exhaust gas is generated by combustion of a fuel and an oxidant having an oxygen concentration of at least 30%.
The method described in. 10. The method of claim 8 wherein the particles comprise the feedstock for a cement kiln. 11. The method of claim 8, wherein the particles comprise the feedstock for a lime kiln. 12. The method of claim 8, wherein the particles comprise iron ore. 13. The high temperature exhaust gas is at least 1500.
9. The method of claim 8 having a temperature of ° F (816 ° C).